This invention relates to an apparatus and a method for facilitating the connection of pipes, and more particularly, but not exclusively, to a powered drill pipe tong for facilitating the connection of sections or stands of drill pipe.
Drill pipe tongs are commonly used for facilitating the connection of sections or stands of drill pipe to a pipe string. Typically, the pipe string hangs in a wellbore from a spider in a floor of an oil or gas rig.
A section or stand of drill pipe to be connected to the pipe string is swung in from a drill pipe rack to the well centre above the pipe string. A pipe handling arm may be used to guide the drill pipe to a position above the pipe string. A stabbing guide may then be used to align a threaded pin of the drill pipe with a threaded box of the pipe string. A drill pipe tong is then used to tighten the connection to a torque of typically 68,000 Nm (50,000 lb.ft).
The drill pipe tong is also used for disconnecting drill pipe. This operation involves breaking the connection which requires a torque typically greater than the tightening torque which may typically be used in the order of 11,000 Nm (80,000 lb.ft).
A drill pipe tong generally comprises jaws mounted in a rotary which is rotatably arranged in a housing. The jaws are moveable relative to the rotary in a generally radial direction towards and away from an upset part of the pipe to be gripped. The upset parts of the pipe are generally located above the pin and below the box of the pipe and have an enlarged outer diameter and/or a reduced inner diameter.
In use, the rotary is rotated forcing the jaws along cam surfaces towards the upset part of the section of pipe. Once the jaws fully engage the upset part, the rotary carries on rotating applying torque to the threads and hence tightens the connection between the section of pipe and the pipe string.
Several problems have been observed with such prior art drill pipe tongs.
In particular, such drill pipe tongs can badly scar the upset part of the pipe, particularly if the jaws start rotating relative to the drill pipe.
Once scarred, the pipe is then lowered into the wellbore. Friction between the wellbore (or casing lining the wellbore) and the scarred upset grinds the upset, reducing the diameter.
Scarring of the upset may also be caused by having to reapply the jaws. This is especially common when connecting pipe with xe2x80x9cwedge threadsxe2x80x9d which requires approximately 80xc2x0 of turn in order to torque the connection. Many prior art wrenching tongs need to be reapplied to the pipe every 25xc2x0.
A reduction in diameter of the upset requires the use of a drill pipe tong or for the old drill pipe tong to be modified therefor.
An attempt at solving this problem is disclosed in PCT publication Number WO 92/18744, which discloses a rotary comprising hydraulically operated active jaws and stationary passive jaws. The hydraulically activated jaws are engaged fully with the pipe prior to rotation of the rotary, thereby substantially reducing scarring. A hydraulic circuit is provided on the rotary for actuating the jaws. A plunger is used to activate the hydraulic system by depressing a hydraulic piston of the hydraulic circuit repeatedly. This operation takes time. If several seconds can be saved per connection, the overall cost of the construction of an oil or gas well can be drastically reduced, as long as reliability is not sacrificed.
Another problem associated with the rotary disclosed in PCT Publication Number WO 92/18744 is that repeated depressing of the plunger for engaging the jaws fully with the pipe may itself cause some scarring.
A further problem associated with power tongs is how to move jaws into engagement with a tubular with sufficient force and sufficient speed.
A still further problem associated with a rotary for power tong is how to fit a mechanism for applying jaws to a tubular into the confined space of a rotary. In particular, the problem arises that if a pump is provided on the rotary for pumping hydraulic fluid, the means of supplying power to the pump must be disconnected before the rotary can be rotated to torque the connection between pipes. This further adds to the overall time of the operation.
If a pump is not provided on the rotary, the hydraulic pressure must be provided via a hose attached to the rotary, and this also must be disconnected before the rotary can be rotated.
Accordingly, a first aspect of the invention provides an apparatus for facilitating the connection of pipes, which apparatus comprises a rotary (4) and a stator (5), said rotary (4) comprising at least one jaw (24,25,26), at least one piston (15,16,17) arranged in at least one cylinder (18,19,20) for actuating said at least one jaw (24,25,26), and a hydraulic circuit (100) linking a first chamber in front of said piston (15,16,17) and a second chamber to a rear side of said piston (15,16,17) such that, in use, hydraulic fluid is expelled from one of said first or second chambers and replenishes the other of said first and second chambers.
Other features of the first aspect of the invention are set out in claims 2 to 12.
There is also provided a method for facilitating the connection of pipes, comprising engaging a motor attached to a stator with a pump attached to a rotor and transferring rotational energy from the motor to the pump, enabling the pump to drive hydraulic fluid to actuate at least one jaw. In a preferred embodiment, the method comprises the step of moving the motor from a first position in which it is disengaged from the pump to a second position in which the motor and the pump are engaged to transfer rotational energy from the motor to the pump. A second aspect of the invention provides an apparatus for facilitating the connection of pipes which apparatus comprises a rotary and a stator, said rotary comprising at least one jaw, at least one piston arranged in at least one cylinder for actuating said at least one jaw, and a hydraulic circuit linking a first chamber in front of said piston and a second chamber to a rear side of said piston such that, in use, hydraulic fluid is expelled from one of said first or second chambers and replenishes the other of said first or second chambers.
There is also provided a method for facilitating the connection of pipes, the method using the apparatus of the first aspect of the invention, the method comprising the step of expelling hydraulic fluid from one of said front or rear sides of said piston and replenishing the other of said front or rear sides of said piston.
A third aspect of the invention provides an apparatus for facilitating the connection of pipes which apparatus comprises a rotary and a stator, said rotary comprises at least one jaw and at least one piston arranged in at least one cylinder for actuating said at least one jaw, and a hydraulic circuit, wherein said hydraulic circuit comprises a valve preventing return flow of hydraulic fluid and a restriction such that, in use, the arrangement allows a finite force to be applied to said pipe.
There is also provided a method for facilitating the connection of pipes, the method using the apparatus of the second aspect of the invention, the method comprising the step of allowing hydraulic fluid to leak from said hydraulic circuit such that said at least one jaw applies a finite force to said pipe.